Are you running Magento version before 2.0.6.? Time to upgrade!
It was recently discovered that all Magento versions before 2.0.6. (both Community and Enterprise Edition) are vulnerable against an unauthenticated Remote Code Execution. The vulnerability (CVE-2016-4010) could allow an attacker to take over the vulnerable process, consequently even take complete control over the machine, putting your customer data, transaction history and revenues at risk.
[Solution] Upgrade to the 2.0.6 patch as soon as possible